Arguments

Character vector providing set of allowed levels. if NULL,
will generate levels based on the unique values of x, ordered by order
of appearance in x.

ordered

Is it an ordered factor?

na

Character vector of strings to use for missing values. Set this
option to character() to indicate no missing values.

locale

The locale controls defaults that vary from place to place.
The default locale is US-centric (like R), but you can use
locale() to create your own locale that controls things like
the default time zone, encoding, decimal mark, big mark, and day/month
names.